The present invention relates to a turbo-supercharger for an internal combustion engine.
For turbo-superchargers commonly used with internal combustion engines, the flow rate of exhaust air at low engine speed generally is insufficient resulting in less than satisfactory performance. More specifically, the ratio P.sub.2 /P.sub.1 between inlet pressure and outlet pressure with respect to the flow rate of exhaust gas to the turbo-supercharger varies as shown in FIG. 4. Since the efficiency of a supercharger's turbine is expressed by n=1-(P.sub.1 /P.sub.2).sup.K-1/K, the ratio of inlet pressure and outlet pressure substantially affects efficiency with increased inlet pressure providing increased turbine efficiency. Accordingly, for internal combustion engines exhibiting large variations in exhaust gas flow rates, it is very difficult to effectively utilize exhaust energy for intake supercharging when using a single turbine.
Laid-Open Japanese Utility Model Application No. 114844/1983 discloses an arrangement wherein a turbine disc possesses both a low-speed disc and a high-speed disc disposed internally and externally, respectively. In addition, exhaust air flow to the turbine is controlled by a valve which interrupts flow to the high-speed disc when the flow rate of exhaust gas is small. Although improving efficiency, the aforesaid arrangement is relatively complicated in construction and high in cost. Moreover, a partitioning wall for separating passages connected to the high-speed and low-speed turbine discs is cast integral with a turbine housing resulting in a partition of undesirably great wall thickness. Consequently, if a heat insulating material is mounted on these internal wall surfaces, the passages become unduly narrowed.
The object of the present invention, therefore, is to provide a turbo-supercharger which is small in size, provides high efficiency and can be easily manufactured.